That ugly lamp you almost threw away? It sold for $3,200 at auction last month. And those "worthless" costume jewelry pieces your mom kept in a shoebox? Turns out three of them were signed Miriam Haskell brooches worth $800 each. You're standing in a house packed with 40 years of belongings, and honestly, you have no idea what you're looking at. The stuff that looks expensive might be garage...